This invention relates generally to power mowing apparatus and more particularly concerns improved apparatus for rapidly braking a rotary lawn mower blade or the internal combustion engine which drives it.
Presently used methods of braking the blade of a rotary mower normally involve either an ignition shorting switch adapted to ground the magneto output or spark plug center electrode to the engine block or closure of a valve which provides fuel to the carburetor of the internal combustion engine driving the mower. Each of these methods works on the principle that either cutting fuel to the system or cutting the spark available to ignite the fuel-air mixture in the system will rob the internal combustion engine of continued power. The result will be that the frictions of the system, together with drag on the rotary blade, will eventually act to brake the blade and cause blade rotation to cease. The normal maximum rotation rate of the blade of a rotary mower is of the order of 2400-3500 RPM. Because of this rapid rate and the inertia in the system, the time required to brake the blade using these methods may be longer than desired. It may, for example, be longer than the time required for a person to reach the mower after the mower operator recognizes that the person is approaching.
In addition to the desirability of having a braking time less than this "approach time, " it is advantageous if it is possible to significantly brake the rotary mower blade in the amount of time normally required for the operator to leave the operating position at the end of the control handle and reach the vicinity of the rotating blade. If braking times within these constraints can be achieved, a dead man handle may be used to actuate the braking apparatus. When such an arrangement is used, the dead man handle will automatically actuate the braking apparatus when an opeator releases the control handle, for example, for the purpose of approaching the mower to remove the grass catching bag, to unclog the mower or for some other purpose. This is a desirable safety feature since the blade may be stopped by the apparatus before an unthinking operator can leave his position at the handle and injure himself by contact with the blade.
The present invention overcomes the disadvantage of long braking times associated with prior art apparatus in which the friction in the engine and linkage is used to brake the rotary mower blade. In addition, the present invention provides apparatus which stops the rotary mower blade in an amount of time of the order of the normal time between release of control handle pressure and contact between an operator and the machine housing.